Vibrational relaxation rates in the direct simulation Monte Carlo method

Gimelshein, Natalia; Gimelshein, S. F.; Levin, Deborah A.

doi:10.1063/1.1517297

Cited by 93 publications

(46 citation statements)

References 6 publications

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“…10 Following Haas et al, 19 multiple relaxation events were prohibited. The methodology for selecting relaxing particles was that of Gimelshein et al 20 For simplicity, constant relaxation probabilities of 0.30 and 0.01 for rotation and vibration, respectively, were used. The code employed the downstream piston boundary condition, 1 and particles entering the simulation domain across the upstream boundary were generated according to the method of Ref.…”

Section: Strong Shock In Dissociating Nitrogenmentioning

confidence: 99%

A macroscopic chemistry method for the direct simulation of gas flows

Lilley

Macrossan

2004

Physics of Fluids

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In most chemistry methods developed for the direct simulation Monte Carlo ͑DSMC͒ technique, chemical reactions are computed as an integral part of the collision simulation routine. In the macroscopic chemistry method developed here, the simulation of collisions and reactions are decoupled in that reactions are computed independently, after the collision routine. The number of reaction events to perform in each cell is calculated using the macroscopic reaction rates k Ϯ and equilibrium constant K*, with local macroscopic flow conditions. The macroscopic method is developed for the symmetrical diatomic dissociating gas. For each dissociation event, a single diatomic simulator particle is selected with a probability based on its internal energy, and is replaced by two atomic particles. For each recombination event, two atomic particles are selected at random, and are replaced by a single diatomic particle. The dissociation energy is accounted for by adjusting the translational thermal energies of all particles in the cell. The macroscopic method gives density profiles in agreement with experimental data for the chemical relaxation region downstream of a strong shock in nitrogen. In the nonequilibrium region within the shock, and along the stagnation streamline of a blunt cylinder in rarefied flow, the macroscopic method gives results in excellent agreement with those obtained using the most common conventional DSMC chemistry method in which reactions are calculated during the collision routine. The number of particles per computational cell has a minimal effect on the results provided by the macroscopic method. Unlike most DSMC chemistry methods, the macroscopic method is not limited to simple forms of k Ϯ and K*. Any forms may be used, and these may be any function of the macroscopic conditions. This is demonstrated by using a two-temperature rate model, and a form of K* with a number density dependence. With the two-temperature model, the macroscopic method gives densities in the post-shock chemical relaxation region that also agree with the experimental data. For a form of K* with a number density dependence, the macroscopic method can accurately reproduce chemical recombination behavior. In a primarily dissociative flow, the number density dependence of K* has very little effect on the flow. The macroscopic method requires slightly less computing time than the most common DSMC chemistry method.

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Section: Strong Shock In Dissociating Nitrogenmentioning

confidence: 99%

A macroscopic chemistry method for the direct simulation of gas flows

Lilley

Macrossan

2004

Physics of Fluids

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“…Multiple relaxation events were prohibited, and constant exchange probabilities of 0.3 and 0.01 were used for rotation and vibration respectively. The logic of Gimelshein et al [9] was used to select inelastic collisions. The time step ∆t was 3( 743 ) 100 7 s, and the sampling interval was 7∆t.…”

Section: The Macroscopic Chemistry Methodsmentioning

confidence: 99%

Modeling Dissociation-Vibration Coupling with the Macroscopic Chemistry Method

Lilley¹,

Macrossan²

2005

AIP Conference Proceedings

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Abstract. We test the recently developed macroscopic approach to modeling chemistry in DSMC, by simulating the flow of rarefied dissociating nitrogen over a blunt cylinder. In this macroscopic method, chemical reactions are decoupled from the collision routine. Molecules are chosen to undergo dissociation at each time step, after the collisions are calculated. The required number of reaction events is calculated from macroscopic reaction rate expressions with macroscopic information taken from the time-averaged cell properties. One advantage of this method is that "state-of-the-art" macroscopic information about reaction rates can be used directly in DSMC in the same way as in continuum codes. Hybrid Navier-Stokes/DSMC codes can therefore easily use the same chemical models in both rarefied and continuum flow regions. Here we show that the macroscopic method can capture dissociation-vibration (DV) coupling, which is an important effect in vibrationally cold blunt body flows because it results in increased surface heat fluxes. We use the macroscopic method with Park's two-temperature rate model, often used in continuum studies, to capture DV coupling in DSMC. This produces a flowfield in reasonable agreement with that calculated using the conventional collision-based threshold line dissociation model.

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“…3 Traditionally continuous rotational and vibrational temperatures are used in DSMC to represent the integral modes of molecular species and the Larsen-Borgnakke model 6 is most often implemented in DSMC to model the vibration-translation (VT) energy transfer. In the work of Gimelshein et al, 7 the relaxation probability in the LB model was defined as P = 1/Z v where Z v is the vibrational relaxation number which is a function of the number of vibrational degrees of freedom and varies with temperature. The work 7 derived the exact relationship that connects the vibrational relaxation number, Z v used in DSMC with that employed in continuum simulations.…”

Section: Introductionmentioning

confidence: 99%

DSMC Modeling of NO Formation for Simulation of Radiation in Hypersonic Flows

Sohn

Levin

2012

50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition

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The current work has implemented in DSMC discrete vibrational levels of N2 and the transitions between them as well as the dissociation of nitrogen molecules and formation of NO molecules. The vibration-translation transition models assessed include LarsonBorgnakke, Schwartz-Slawsky-Herzfeld (SSH), and Forced Harmonic Oscillator (FHO) models. Total Collision Energy (TCE) and QCT models for the NO formation reaction are considered. The effect of the models on the flowfield is explored and comparisons are made. Improved NO radiation modeling is proposed by employing quenching rates from most-recent experiments. Comparisons of electronic state populations and the corresponding radiative spectra among the neutral-impact excitation models are made. It is validated that vibrational band spectral structure of NO radiation is strongly influenced by vibrational temperature profiles along a line of sight.

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Vibrational relaxation rates in the direct simulation Monte Carlo method

Cited by 93 publications

References 6 publications

A macroscopic chemistry method for the direct simulation of gas flows

A macroscopic chemistry method for the direct simulation of gas flows

Modeling Dissociation-Vibration Coupling with the Macroscopic Chemistry Method

DSMC Modeling of NO Formation for Simulation of Radiation in Hypersonic Flows

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